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Old 2020-04-04, 19:22   #1
kriesel
 
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Default Filtering out dumb mask ideas.

https://www.youtube.com/watch?v=1r2C1zGUHbU

I'm skeptical of the effectiveness of the folding as shown.
(1) The fold sequence in the video puts 3 layers of horizontal seam (gap) right in the middle (equator), resulting in a stripe of single-ply cloth, before the ends are folded toward center.

(2) Consider a horizontal W fold instead of the sequence shown, which produces 4-ply with no midline ("equatorial") seam/gap in any of the layers. But maybe upper and lower edges are an issue in that case, if air enters at upper and lower edges and passes through only 1 or 2 plies.

(3) Starting from flat, fold top 1/8 down behind. At 1/4 of original height down from that fold, fold the lower (5/8) portion up and over. Fold original bottom 3/8 down and over. Fold bottom 1/8 down and under. Pull original top 1/8 out from behind, up and fold down and over. This results in 3-ply at the horizontal midline, 4-ply everywhere else, and closed top and bottom edges.

The effectiveness is probably limited by poor sealing to the face for any of these, compared to a properly used N95 mask, but might be comparable to a PM2.5 which also looks to have limited sealing.
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Old 2020-04-04, 19:42   #2
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My sister gave me 4 earloop masks from a 25-box she had last week, even blasting them with hot air after use (note - mustn't be too hot, much above 100C the thin plastic guazy-film on the outside melts) they last perhaps 2,3,4 days.

Looking to lay in my own stash, yesterday I found earloop masks widely available on Amazon, but ship dates vary hugely, I had to dig a bit to find the following, both with an April 10-20 ETA:

https://www.amazon.com/Disposable-3-.../dp/B086MNRBZ8

https://www.amazon.com/Washable-Earl.../dp/B086MW19JG

I ordered 1 of each.
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Old 2020-04-04, 20:14   #3
a1call
 
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Are both the inlet and discharge to and from a N95 mask (or any other valved mask) filtered?
I would assume not. If so then how effective would they be in preventing the infected individuals who are wearing them from infecting others who are not?
Thanks.

ETA A valve in a face mask can only make sense as a Check-Valve which works like a diode, allowing current in one direction while blocking it in the other.
If both inlet and outlet are to be filtered, there world be no function for a valve, assuming bidirectional equivalence of filters used.

ETA II
Quote:
The use of an exhalation valve reduces exhalation resistance, which makes it easier to breathe (exhale). Some users feel that a respirator with an exhalation valve keeps the face cooler and reduces moisture build up inside the facepiece.
https://www.cdc.gov/niosh/npptl/topi...ealthcare.html

ETA III How counterproductive is it for potentially asymptomaticly infected staff to wear such "comfortable" valved masks in hospitals and nursing homes? Could this be partly the reason for high infection and mortality rates in such establishments?

Last fiddled with by a1call on 2020-04-04 at 20:31
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Old 2020-04-04, 23:09   #4
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Quote:
Originally Posted by a1call View Post
Are both the inlet and discharge to and from a N95 mask (or any other valved mask) filtered?
Filters worth considering in this application and many others are structured to knock out big particles first, then progressively smaller in succeeding layers. The big stuff is caught mechanically, the very small stuff electrostatically. Electrostatic capture allows catching particles that are smaller than the openings in the filter layers. Such filter structures are by design directional, whether they have valves or not. Filters have service life depending in part on particle loading; eventually the flow resistance goes too high and it's time to change to a new one.
An unvalved N95 mask such as was commonly used in construction and spray painting is unpleasant to wear for extended periods because of the increased breathing effort. If a health care worker is working with known-infected patients, the mask is there to protect the caregiver, and check valves will enable them to work a longer shift.
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Old 2020-04-05, 00:28   #5
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Quote:
Originally Posted by kriesel View Post
If a health care worker is working with known-infected patients, the mask is there to protect the caregiver, and check valves will enable them to work a longer shift.
I think that is a valid point, but it does not address the potentially common case of staff in nursing homes from infecting elders with compromised immune systems. I think there are remedies to the problematic unidirectional protection. While inhaling bleach fumes is probably more harmful than any coronavirus can ever be, perhaps a bleach-soaked low resistance membrane on the discharge side of the check valve can create a layer of protection to the patents/elders without inconveniencing the staff. Clearly measures in place at the moment do not seem to offer much protection in nursing homes at the moment.

Last fiddled with by a1call on 2020-04-05 at 00:30
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Old 2020-04-05, 19:06   #6
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Quote:
Originally Posted by a1call View Post
While inhaling bleach fumes is probably more harmful than any coronavirus can ever be, perhaps a bleach-soaked low resistance membrane on the discharge side of the check valve can create a layer of protection to the patents/elders without inconveniencing the staff.
That may be worse for everyone than not doing so. Bleach is typically a chlorine source. Chlorine was used in chemical warfare in WWI. Voluntarily wearing bleach soaked fabric an inch or two from the mask's intake may be a very bad move, creating a preexisting condition in the lungs of the caregiver, that many pathogens could take advantage of. What's exhaled does not simply disappear; the last of it and whatever it picks up on its exit is right there in front of the mask when the exhale ends and the inhale begins. Oxidizers like ozone and chlorine are very bad to inhale. https://en.wikipedia.org/wiki/Bleach#Health_hazards
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Old 2020-04-05, 19:54   #7
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Quote:
Originally Posted by kriesel View Post
That may be worse for everyone than not doing so. Bleach is typically a chlorine source. Chlorine was used in chemical warfare in WWI. Voluntarily wearing bleach soaked fabric an inch or two from the mask's intake may be a very bad move, creating a preexisting condition in the lungs of the caregiver, that many pathogens could take advantage of. What's exhaled does not simply disappear; the last of it and whatever it picks up on its exit is right there in front of the mask when the exhale ends and the inhale begins. Oxidizers like ozone and chlorine are very bad to inhale. https://en.wikipedia.org/wiki/Bleach#Health_hazards
Well, the discharge can be directed/moved-away from the inlet of need be, and another point is that since the inlet is filtered it will filter out the bleach fumes since it is designed to do so anyway.

Here is a recommendation from the web for filtering bleach:

Quote:
For the filter cartridge, you will need a combination of a multi-gas cartridge and a P100 (HEPA) filter to protect you from the bleach vapors and mold spores respectively. The filter cartridge that does this the best is the 3M 60926 Multi-Gas/P100 Cartridge.
https://pksafety.com/blog/a-respirat...leach-and-mold

Last fiddled with by a1call on 2020-04-05 at 20:02
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Old 2020-04-05, 20:41   #8
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For tier record N95 designation is not meant to filter out fumes:
Quote:
Gas molecules, however, range in size from only 0.0003 - 0.006 microns. As a result, gases like oxygen, chlorine, hydrogen sulfide and ammonia can all pass freely in the spaces between the fibers in an N95 mask.
https://www.massnurses.org/health-an.../openItem/1318
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Old 2020-04-06, 03:10   #9
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Quote:
Originally Posted by a1call View Post
Well, the discharge can be directed/moved-away from the inlet of need be, and another point is that since the inlet is filtered it will filter out the bleach fumes since it is designed to do so anyway.

Here is a recommendation from the web for filtering bleach:

https://pksafety.com/blog/a-respirat...leach-and-mold
So now your "solution" is to require the particulate mask be upgraded to a gas mask too, presumably also equipped with integral goggles covering the eyes of the nurse or doctor from the chlorine?! And the "inlet" is nearly the entire outer surface area of the N95 mask, excluding only the check valve area and the area outside the face seal. To separate the wearer's air intake and exhaust for this scheme there's probalbly a snorkel-like duct. The chlorine from the bleach is not only a threat to the mask wearer, but to the patients nearby, who already have substantial respiratory issues that put them there. N95s cost less than $1. Rubber gas masks cost many times that. Particulate filtration and gas removal cartridges add to the cost. There are probably not enough in the world. Cost is a measure for manufacturing effort. They'd have to be sterilized or replaced frequently. They're heavy, hot, and uncomfortable, to a whole other level.
I think someone with an understanding of fluid mechanics would know your proposal is unworkable.

Consider the possibility that the people who design the PPE measures know what they're doing.

Last fiddled with by kriesel on 2020-04-06 at 03:27
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Old 2020-04-06, 03:35   #10
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Quote:
Originally Posted by ewmayer View Post
Re. the N95 exhalation-valve issue - can one wear one of the thin 3-ply surgical masks being recommend for hoi polloi either under or over the N95 one?
Possibly surgical over N95. Intake resistance is increased, as is exhale resistance, and mask consumption rate. Surgical under N95 would defeat the face seal of the N95. Does the surgical over N95 interfere with the check valve action? No samples here to examine.

Last fiddled with by kriesel on 2020-04-06 at 03:36
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Old 2020-04-06, 04:07   #11
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I might not have been clearly stating it but I was referring a novel design, not an upgrade of existing N95 masks which seem to have turned the nursing homes into slaughter houses for the the elderly around the world.
My point is that a mask can be designed that is a bit more secure than the idiotic valved masks which offer no protection whatsoever to the patients who are treated with staff who are wearing them. The bleach soaked membrane is a valid idea that I suggested as a means of offering limited protection if the check valves are to be used. The bleach fumes are hazardous and I acknowledged it in the first post I made on the subject stating it was more harmful than coronavirus. But the exposure to the patents could perhaps be minimal given the small area of the discharge and the air circulation. There are of course better solutions such as increasing the surface area of the discharge filter of any kind and thus reducing the discharge resistance.
The increased cost of properly destined gear for very few nursing home staff in any given population is probably a fraction of the money governments around the world have pledged to spend.

BTW for the record, inlet/outlet related design in industrial-settings is what I do as my day job and have been doing for the last 9 years.

Last fiddled with by a1call on 2020-04-06 at 04:10
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